1. Field of the Invention
This invention relates to an internal measuring instrument for directly measuring wall thickness and for detecting flaws within the wall of a tube. The present invention can be used in any straight or curved tubular structure but is especially useful in long tubes or tubes featuring bends and U-turns.
2. Description of the Prior Art
Periodic inspection and measurement of the wall thickness and internal wall characteristics of tubular structures such as boiler tubes, metal pipes or casings are important in order to determine whether any corrosion or bulging of the pipe has occurred. It is also necessary to periodically check tubes and conduits for the presence of flaws, such as inclusions, to insure that the tubes can withstand a certain amount of pressure. For boiler tubes in particular, measurement of the wall thickness enables the location and extent of corrosion to be ascertained and provides information useful in ascertaining when replacement is required.
Various types of instruments for measuring the wall thickness of pipe or for measuring the internal characteristics of tubular structures have been heretofore proposed. One type includes a support housing having a number of feeler arms for engaging the inner wall of the tubular structure as the housing is moved longitudinally therethrough. The movement of each feeler arm then serves to drive a recording pen on a drum-type recording chart contained in the housing. This type of apparatus has the disadvantage that the results of the measurements are not immediately available to the operator and thus the operator has no way of knowing whether the apparatus is operating correctly until after the run has been completed.
Another type of previously proposed apparatus for measuring internal dimensions includes a number of feeler arms mechanically coupled to a common electrical element, such as potentiometer, for adjusting the electrical characteristics thereof. The variation of such electrical characteristics controls an electrical signal which is developed and transmitted to a recording unit at the exterior to the tubular structure. This type of apparatus suffers from the disadvantage that adjustment of the common electrical element is usually restrained by the particular feeler arm which is displaced by the least amount. Consequently, the resulting indication relates only to the minimum dimension in a single direction and does not afford any indication of the shape of the inner wall in a circumferential sense. As a result, such an indication does not afford a complete picture of the cross-sectional shape of the tubular structure.
A third measuring apparatus is disclosed in U.S. Pat. No. 2,994,962 (1961), entitled: "Tubing Measuring Apparatus Using Pulse Sequences." This device uses transducer means coupled to a plurality of feeler members for repetitively developing a sequence of output signals. Each pulse in the sequence is representative of the displacement of a different one of the feeler members, thereby providing a continuous presentation of the internal characteristics of a tube. This apparatus differs from the disclosed invention by not measuring flaws within the wall of pipes or tubes. This apparatus also is limited to measuring internal dimensions in straight tubes and would have a hard time negotiating curved tubing.
The general object of this invention is to provide a new and improved internal measuring instrument for measuring the wall thickness of pipes and tubes.
A more specific object of this invention is to provide an internal measuring instrument which can measure the wall thickness of tubes which contain bends and curvatures along their length.
A further object of this invention is to provide an internal measuring instrument for detecting flaws within the walls of a tube by using pulse echo transducers.
Still further, an object of this invention is to provide an internal measuring instrument which is responsive to signals from at least one transducer unit attached to a rotatable disc held in pressure contact with the inner wall of a tube wherein interpretable and continuous indication of the thickness of the wall can be observed.
Other objects and advantages will become apparent to one skilled in the art based upon the ensuing description.